Liquid solutions are currently used in the calibration and quality control of sensors, and these reagents are typically stored in closed systems such as glass ampoules or laminate barrier pouches, where the barrier material serves to prevent interaction with the environment and thus maintain a pre-determined amount of gas in the solution (see for example, U.S. Pat. No. 6,632,675, issued to Conlon et al. on Oct. 14, 2003; and U.S. Pat. No. 6,136,607, issued to Conlon et al. on Feb. 3, 1998; the entire contents of each of which are expressly incorporated herein by reference). However, the shelf life of these solutions may be limited as a result of degradation products, such as but not limited to, ammonia and carbon dioxide.
When urea is present in solution, it degrades into ammonia and carbon dioxide (CO2), particularly upon storage for extended periods of time at non-refrigerated storage temperatures. Generation of ammonia within the solution significantly increases and destabilizes the pH of the solution, thus reducing the shelf life of the solution and limiting the temperature options available for storage of the solution.
Urea-containing solutions are also utilized for protein/peptide processing. Another urea degradation product, cyanate, can react with the proteins/peptides to be processed and thus interfere with the protein/peptide processing reaction. Carbamylation of a protein/peptide occurs when cyanate reacts with certain amino acid side chain functional groups, thus yielding a carbamylated protein/peptide derivative that may have different biological and/or antigenic properties when compared to the native protein/peptide. Methods of inhibiting protein carbamylation in urea-containing protein/peptide processing solutions have been disclosed (see, for example, U.S. Pat. No. 4,605,513, issued to DiMarchi on Aug. 12, 1986; U.S. Pat. No. 7,459,425, issued to Wan and Ropp on Dec. 2, 2008; and US Published Application Nos. 2005/0032153 and 2012/0007022, published to Ropp et al. on Feb. 10, 2005 and Jan. 12, 2012, respectively; the contents of each of which are incorporated herein by reference in their entirety). In these methods, a cyanate scavenger molecule is added to a 7-9 M urea protein/peptide processing solution (at a final concentration of 1 mM to 150 mM for the scavenger); examples of cyanate scavengers disclosed by these references include, but are not limited to, 1,2-ethylene diamine and 1,2-ethylene diamine-like materials; diethanolamine; amino acids and amino acid derivatives such as but not limited to, L-Arginine, L-Cysteine, L-Glycine, L-Histidine, L-Lysine, L-threonine, taurine, glycinamide, and 4-hydroxy-proline; the dipeptides glycylglycine (Gly-Gly), histidylglycine (His-Gly), and histidylglycine (His-Gly); and the tripeptide tri-glycine (Gly-Gly-Gly). However, the effect of a cyanate scavenger molecule on the pH of these high molarity urea solutions has not been determined.
Therefore, there is a need in the art for new and improved aqueous urea-containing reagent embodiments used in the calibration and quality control of sensors that provide pH control thereof and thereby exhibit extended shelf life and temperature storage options for the reagents.